The objective of the proposed research is to ascertain whether the size of mineral fibers, such as asbestos and fibrous glass preparations, is a determinant of the development of cancer, as assayed by epithelial cell responses in vitro. Using previously developed techniques that quantitate hyperplasia induced in vitro by asbestos, a series of well-characterized fibers will be studied. Data from long-term in vivo exposure to seventeen fibrous glass preparations yielded information correlating fiber size to the development of cancer. These, and other fibers, will be studied. This research aims to determine if this experience can be replicated in a short-term culture system, and if a hyperplastic response can be used as a predictor of carcinogenicity. Trachea explants from hamsters are maintained in a chemically defined culture medium, based on CMRL-1066. They are kept in gas-tight boxes in an atmosphere of 5% CO2, 50% oxygen, and 45% nitrogen, and rocked back and forth twelve times per minute. After two days to allow stabilization, the fibers to be studied are added to the cultures in fresh culture medium, at a concentration of 1mg/ml. The tracheas are harvested, and fixed in buffered formalin, after observation periods of 24 to 96 hours. Embedded in plastic, two micron sections are prepared and stained with H&E, or processed for autoradiography. Using image analysis appratus quantitated cell counts are obtained and the data analyzed statistically to verify if hyperplasia has occurred. This research would help evaluate the question of fiber size to carcinogenicity, and perhaps allow for rapid evaluation of carcinogenicity of inorganic fibers. Further, the accuracy of hyperplasia induced in a culture system for prediction of neoplasia will be evaluated.